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AJvYcCXRQoePIsCz1tffVK3VhGZ8vsx8z5OoLyA9MT+X+2D6+WTKywZRlJazxueQYj7EjDxAVc1kQs5Wgtc=@lists.xenproject.org X-Gm-Message-State: AOJu0Yy4TrxD9lNn9WwgZxPgEKsF7ugxXMzC2KgHK/QZTpX6qXzVMHPP 4AD4/bynezyeCTjudIi37BlO8VYLSxqJWPXk8uiskOi7oQjJMVEl6bEfojqPflLKUG44kJ/DbZJ J X-Google-Smtp-Source: AGHT+IHZX06NFgcBX6G648tacbpfWhzBgix2ljoVffnzG5deVBE5CD7J8Rc6Xk1lMh5AJMl1R4LjcQ== X-Received: by 2002:a05:6402:348c:b0:5c9:5c8a:99e5 with SMTP id 4fb4d7f45d1cf-5ceb936a3d1mr364885a12.30.1730395077724; Thu, 31 Oct 2024 10:17:57 -0700 (PDT) Message-ID: <6877d26c-144f-4b4e-968c-28b535cb3db1@citrix.com> Date: Thu, 31 Oct 2024 17:17:55 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/mm: ensure L2 is always freed if empty To: Roger Pau Monne , xen-devel@lists.xenproject.org Cc: Jan Beulich References: <20241030114852.55530-1-roger.pau@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: <20241030114852.55530-1-roger.pau@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 30/10/2024 11:48 am, Roger Pau Monne wrote: > The current logic in modify_xen_mappings() allows for fully empty L2 tables to > not be freed and unhooked from the parent L3 if the last L2 slot is not > populated. > > Ensure that even when an L2 slot is empty the logic to check whether the whole > L2 can be removed is not skipped. > > Signed-off-by: Roger Pau Monné > --- > I've attempted to find a Fixes tag for this one, but I'm afraid there have been > many changes in the function, and it's possibly the code that introduced the L2 > freeing (4376c05c31132) the one that failed to originally adjust this case. > --- > xen/arch/x86/mm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c > index d537a799bced..0f53dcebad95 100644 > --- a/xen/arch/x86/mm.c > +++ b/xen/arch/x86/mm.c > @@ -5717,7 +5717,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf) > > v += 1UL << L2_PAGETABLE_SHIFT; > v &= ~((1UL << L2_PAGETABLE_SHIFT) - 1); > - continue; > + goto check_l3; > } > > if ( l2e_get_flags(*pl2e) & _PAGE_PSE ) https://gitlab.com/xen-project/hardware/xen/-/jobs/8240163332 That's hitting the BUG_ON(!nr_bootmem_regions); in alloc_boot_pages().   [] R alloc_boot_pages+0x46/0xbc   [] S alloc_xen_pagetable+0x5e/0x60   [] F alloc_mapped_pagetable+0xd/0x3e   [] F arch/x86/mm.c#virt_to_xen_l2e+0x78/0xec   [] F map_pages_to_xen+0xefb/0x1079   [] F arch/x86/setup#bootstrap_map_addr+0x95/0xff I think what's happened is you've "freed" l2_bootmap[], causing bootstrap_map_addr() to now need to allocate memory. I've reverted for now, per Roger's request on Matrix. ~Andrew